The present invention relates generally to data storage devices and more specifically, to apparatus and methods for testing components of magnetic disk drives.
Magnetic disk drives are typically composed of components such as read/write heads, actuators, magnetic disks, spindle motors, printed circuit board assemblies and firmware. These components are tested during manufacturing using one or more component testing machines to ensure that they meet the specified performance requirements. Depending on the component being tested, the tests typically measure the component's performance with respect to timing, reading, writing, motor control and servo positioning.
However, the use of conventional component testing machines to test drive components is very costly due to their complicated electrical and mechanical designs. Conventional testers typically have used expensive precision, custom-made components such as mechanical positioning stages, stepper motors, discrete channels, air-bearing spindle motors and motor plate mechanics.
In addition, conventional testers have been typically designed with little consideration of the disk drive environment. The testers' electronics typically were customized to meet the component frequency testing requirements. The testers' mechanics typically were customized to provide the best run-out control without considering high-speed run-out canceling. Further, the testers' software was typically designed to work independently of drive control. Thus, conventional testers did not test components in an environment similar to that of an actual disk drive.
As a result, the correlation between the analog test measurements of components obtained with conventional testers and their actual performance in disk drives has been relatively low. This low correlation resulted in relatively high levels of over-rejects and false acceptance of components.
Another disadvantage of conventional testers is that they relied on mechanical positioners to place the head on the written track instead of using a servo control loop. This limited the track control or tracks per inch (TPI) capabilities of these testers. Further, the positioners were not be able to support track-following of high-frequency track misregistration (TMR) because of the low bandwidth inherent to their large mass and size.
Accordingly, there is a need for a tester for magnetic disk drive components that is lower in cost, provides more accurate test results and is capable of testing higher TPI disk drives than conventional testers.